Il6 UNIVERSITY OF COLORADO STUDIES 



sine-labradorite. Calcite, kaolin and sericite are common alteration 

 products. 



There are two kinds of pyroxene present. First, in great amount is 

 very pale brown augite which is faintly pleochroic. The extinction angle 

 measured from the composition plane of the orthopinacoidal twins, 

 which are very common, ranges from 40 to 45 . In a few sections 

 basal parting is distinct. Usually the augite is interstitial between the 

 feldspar laths, generally without a common orientation ; rarely it involves 

 the feldspars, producing true ophitic texture. A few crystals have fairly 

 well-defined crystal outline and are idiomorphic toward even the earliest 

 formed feldspar. The augite is often uralitized; and chlorite, black 

 iron ores, epidote, calcite and quartz are common alteration products. 

 Serpentine in fibrous aggregates is often intergrown with chlorite. 



A second variety of pyroxene, somewhat less in amount, is ortho- 

 rhombic. It is pale yellow, slightly pleochroic, and weakly birefringent. 

 Ordinarily it is more nearly idiomorphic than the augite, though it had 

 not always taken on crystal boundaries before the augite began to 

 crystallize. That it is hypersthene instead of enstatite is indicated by 

 the emergence of the optic axes in the macropinacoid (100). Minute 

 inclusions, colorless to brown and opaque, with their long axes normal 

 to the vertical crystallographic axis, are abundant. Although the 

 hypersthene is usually quite fresh it is sometimes changed to bastite, 

 bright yellowish-green in color, with fibers parallel to the vertical axis 

 of the hypersthene. Other alteration products are uralite, or a mix- 

 ture of uralite and serpentine; frequently serpentine fills fractures 

 passing through the mixture. Sometimes serpentine alone replaces 

 the hypersthene, the process beginning in the cleavage planes. Occa- 

 sionally small specks of limonite stain the surface of the less altered 

 pyroxene. 



By far the greater part of the iron oxide is interstitial, though occa- 

 sionally euhedrons of magnetite are enclosed in the augite. Much iron 

 ore replaces augite, sometimes retaining the crystal outline. More 

 often it is in irregular masses and skeleton crystals. Occasionally it 

 appears to replace biotite. This ore is either ilmenite or titaniferous 

 magnetite, since material removed from the powdered rock by means 



